In its cyber crime report, Europol said the use of encrypted tools, which enable offenders to stay anonymous, were now "becoming the norm".
With millions of children online, access to them was "higher than ever".
Cybercrime reporting in Europe had surpassed traditional crimes, it said.
Europol called the ability for child sex offenders to communicate, store and share materials and hunt for new victims online "one of the internet's most damaging and abhorrent aspects".